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Crayfish are marvelous classroom organisms. They are exciting
and easy to care for. Through close observation, students can
learn interesting details about animal structures while developing
sensitivity to the needs of living organisms. Crayfish can act
like living magnets, keeping students in at recess and drawing
students into your classroom from all over school. In short, crayfish
can bring new life to your classroom.
Crayfish are crustaceans. Their appearance is bizarrethey
are festooned with a bewildering array of walking legs, pincers,
and other appendages for eating, feeling, and attending to other
crayfish business. Equipped with thousands of sensory bristles,
some sensitive to chemicals and the others to touch, crayfish
can smell, feel, and hear acutely, even though they are completely
covered in a hard shell. They are aquatic, but can survive fairly
extended sojourns on dry land as long as their gills remain moist.
In order to meet the crayfish up close and personal, let's review
some of this animal's natural history.
Crayfish like it dark and cool, and during much of the daylight
they will be found alone, withdrawn under a rock or a clump of
vegetation, waiting for dark, at which time they come out to forage
for food. Crayfish are omnivorous, eating just about anything
they can find or catch, dead or alive. Large food is held and
torn to pieces in the large pincers and conveyed to the mouth
by the smaller specialized legs near the head. That's what crayfish
mostly do: loaf all day and look for food all night.
Crayfish are terrific animals for your students to study. They
walk, swim, eat, hide, breathe, mate, molt, and die right in the
classroom. Your crayfish container is a microcosm of life on Earth,
and students will learn a lot by sharing time with crayfish.
Reproduction. But there are times in a crayfish's
life when the routine is broken. Males and females, spurred on
by messages communicated to each other, join periodically for
mating, especially in the spring. Males can be told from females
by the generally larger pincers and narrower tails, but these
characteristics are not absolute. To tell for sure, you must pick
them up and look underneath. Males have two pairs of modified
swimmerets (the small leglike appendages under the tail) that
are white-tipped and lay between the last pair of walking legs.
The females have longer, softer-looking swimmerets (for holding
the eggs) and a little white pore centered between the walking
legs. Some time after mating the female lays about 200 eggs, which
she carries in a mass under her tail.
After several weeks the eggs hatch, and a hoard of minute, perfectly
formed, ravenous baby crayfish emerge. At first they continue
to ride along under the female's tail, eating tiny waterborne
bits of food, but soon they leave this security and head out on
their own. During these early days many are eaten by fish, insects,
and other crayfish, but some always survive to fulfill their destiny.
Pregnant crayfish. You think you might have
a pregnant crayfish? Here are some things to consider.
- A peaceful environment with plenty of cover in or under which
to hide will provide security for the mothers. You might
want to go one step farther and separate the two females so
each has a basin of her own. That way you will be able
to tell whose offspring belong to which female
- When the eggs hatch it will be even more important for there
to be lot of structure in the habitat. Plan to put
in a bunch of plants or even plastic plants in which the babies
can hide. Rocks, pebbles, flower pots, and the like are
good, too. The thing you want is lots of places for the
babies to hide from each other. They are notorious for
eating each other. As you know, crayfish are at risk just
after they have molted, and the little ones love to snack on
their just molted brothers and sisters. That’is
the way it goes in the crayfish world.
- If you have some flake fish food, a little bit crumbled up
into dust will be a good food source for the babies. They
will find the tiny bits that fall into the gravel on the floor
of the habitat.
- One more thing...don't give up on the eggs. It might
be 4–6 weeks before they hatch. You may not know
when your females laid their eggs, in which case it will be
a surprise when they hatch.
Molting. Another ponderable: think about the
problem of living inside a suit of armor. Crayfish can't grow
unless the shell (comprising the carapace, or main body shell,
tail shell, and leg shells) can be removed. And this is exactly
what crayfish do. Periodically (quite often early in life) the
crayfish slides out of its old, hard shell in a process called
molting. The "naked" crayfish that emerges is actually
covered in a complete and perfect shell, but it is soft and flexible,
allowing the crayfish to expand and grow. After a day or so the
new shell will become hard, again affording the animal the protection
of an armored exterior.
In preparation for molting the crayfish withdraws most of the
calcium from its shell, and stores it in two white "tablets"in
the sides of its head. Calcium is a major hardener in the crayfish
shell, as it is in strong human bones and teeth. With this precious
supply of calcium the new shell can harden in a matter of hours
instead of days or weeks.
Ordering crayfish. There are a number of ways to get crayfish
for this activity. Have students catch crayfish from a local creek
or pond; buy them from a bait shop; or order them from a biological
supply company. In any case, you will need 1012 healthy
crayfish that are accustomed to still, relatively warm water (as
opposed to cold, fast-running streams).
If you purchase the crayfish from a biological supply company,
place your order for one dozen medium-size crayfish well before
the investigation. Let the company know on what date you plan
to introduce the crayfish to your class. Use a local vendor if
Preparing for crayfish arrival. A day or two before you
expect the crayfish to arrive, prepare their habitat. Fill two
bus trays about one-third full of cold tap water (34 cm
deep). Keep the trays out of sight in a cool, dark place. Let
the water sit for a day or more to release chlorine from the water.
What to do when they arrive. The crayfish will
arrive in a cardboard box packed with damp paper or moss. Alert
the school secretary to notify you as soon as they come. Immediately
upon arrival, cut open plastic bag to provide air. Keeping bag
upright, float entire contents in prepared bus tray for 15 to
30 minutes to equalize water temperatures. Carefully remove crayfish
from the bag, grasping each from behind to avoid the strong pincers.
Aquatic plants shipped with the crayfish can be rinsed in clean
dechlorinated or spring water and used as both food and "hiding"
places for the crayfish. Maintain at cool room temperatures, out
of direct sunlight.
Handling the crayfish. Practice picking up the crayfish
so that you can demonstrate the proper technique for your students.
Approach the crayfish from behind. Grasp it firmly on the carapace
(body shell) behind the pincers. Pick it up. It may try to reach
back, but don't worryit will not be able to reach you.
Provide aquatic plants. Buy or collect from a local pond
some small aquatic plants for the crayfish. We recommend getting
612 sprigs of Elodea, also known as Anacharis.
(It looks like a little green feather boa.) You can order it from
a biological supply company when you order your crayfish, or you
can pick it up locally at a pet store that deals with fish. If
Elodea is not available, try another inexpensive aquatic
Find a place for the crayfish. Plan where the two bus
trays with the crayfish will reside in your room for up to several
months. They need to be cool, out of direct sunlight, and safe
from being spilled.
Prepare for care and feeding. Crayfish need ample clean,
cool water and sufficient food in order to be healthy in your
classroom. It is virtually impossible to get the water too cold
(short of freezing), but it is easy for it to get too warm. Try
to keep the temperature between 5°C (41°F) and 20°C
You will feed your crayfish protein in the form of dry cat food
that sinks in water. Don't worry if the crayfish don't eat for
a week or two; they will eat when hungry. Always move the crayfish
out of their home tray and into a basin with 34 cm of water
to feed them the dry cat food. Put in one piece of cat food per
crayfish. Leave them there for about 1/2 hour. (If they don't
eat, they aren't hungry.) Then return them to their home tray,
without any of the cat food. The other food source that is always
available is the Elodea that stays with the crayfish in
their home trays.
This feeding routine can be followed every day if the crayfish
are actively eating, and less frequently if they are not. While
they are in the feeding basin, the home tray can be rinsed and
filled with fresh water. This should be done about once a weekmore
often if the water begins to smell bad.
Plan for a new crayfish home. When you have completed
the activities, there are several options for disposing of the
crayfish. Discuss the options with students and together come
up with a plan.
- Set up an aquarium and make the crayfish permanent members
of your classroom community.
- Another class might like to have them for a science resource.
- If some of the students would like to take them home, send
them off, with parental permission, of course.
- If the crayfish were not collected locally, they should not
be released into the local environment.
Resolving the question of what to do with the crayfish can be
turned over to students. They can do research by writing or calling
local experts to find out what they recommend. One expert to talk
to might be the company that supplied the crayfish. Local fish
and game biologists would be another resource for students to
Crayfish pose no health hazard for students. They do not carry
diseases. Occasionally you will see white wormlike animals attached
to the crayfish carapaces and pincers. They are harmless to both
humans and crayfish. They seem to be opportunists, riding along
for a free meal when the crayfish eat.
Oregon Public Broadcasting video on invasive crayfish.
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